The flexible printed circuit board is also called “flexible board”, is a printed circuit made of a flexible insulating substrate, and has many advantages not available to a rigid printed circuit board. For example, the flexible printed circuit board can be freely bent, coiled and folded, and can be arbitrarily arranged according to space layout requirements, and arbitrarily moved, expanded and contracted in a three-dimensional space, thus achieving integration of assembly of components and wire connection. The flexible printed circuit board can be used for greatly reducing the volume of electronic products, and adapts to the need of the electronic products for development of high density, miniaturization and high reliability. Thus, FPC is widely applied in the fields or products of aerospace, military affairs, mobile communication, portable computers, computer peripheral, PDA (Personal Digital Assistant), digital cameras, etc. In a conventional flexible printed circuit board formed by hot-press laminating, because of a heat expansion effect, the positions of pins of the conventional flexible printed circuit board may be deflected; in the application occasion with enormous number of the pins and small spacing, alignment errors may easily occur if the pins are deflected, resulting in poor contact or forming wrong electrical connection.
A chip on film in an LCD panel is used as an example to explain:
An LCD device includes a backlight module and an LCD panel. The LCD panel is provided with a plurality of criss-cross scan lines and data lines; the scan lines or the data lines extend to the edges of the LCD panel to form leads used for connecting with an external circuit board. Because there are enormous scan lines and data lines, and it is difficult to process by a conventional welding process, a chip on flex is generally adopted, and a hot-press laminating mode is adopted for fitting and fixing the pins of the chip on film with the pins of the data lines or the scan lines to form electrical connection. The pins on the conventional chip on film are equally spaced; the corresponding leads on the LCD panel are also equally spaced; the pins and the leads correspond one by one and keep high-precision overlapping; because the spacing among the pins and the spacing among the leads are too small, and the reliability of direct butt joint is not high, a layer of anisotropic conductive adhesive shall be arranged between the chip on film and the LCD panel; conductive particles are included in the anisotropic conductive adhesive; after the flexible printed circuit board and a glass substrate are hot laminated, the spacing among the leads and the pins is minimal; thus, anisotropic conductive adhesive in the middle is extruded, and the conductive particles among the leads and the pins are compacted, deformed and mutually butted to form an electrical pathway; one end of the electrical pathway is butted against with the lead; and the other end of the electrical pathway is butted against the pins to realize the electrical connection among the leads and the pins. The spacing among the leads and the pins is large, the conductive particles are still in a loose state, and the conductive particles are almost separated; thus, two adjacent leads or pins will not be short-circuited and the reliability of the electrical connection is enhanced.
The problem in the prior art is that: the expansion coefficient of colloid material among the leads on the flexible printed circuit board, such as chip on film, etc., is large; so during hot bonding, enormous heat of a laminating head may cause that the leads are not equally spaced; for the chip on film, the expansion extent of the corresponding LCD panel is small, resulting in that the pins of the chip on film and the leads of the LCD panel are difficult to better overlap, and signal transmission is abnormal.